ID of uer-sender can be easy taken - just send any message from this user to our bot, connected by Stealth with script from examples. In Sysjournal will come message like
17:27:37:759 [Test - Test]: Telegram Message incoming from "Vizit0r" (SenderId: 435486649) : testtest
where 435486649 is sender ID. (id - fake, given for example).